1. Field of the Invention
This invention relates to communication apparatus including radio frequency (RF) circuits and, more particularly, to transceiver systems.
2. Description of the Related Art
High performance wireless communication apparatus such as RF receivers, transmitters, and transceivers typically include RF front-end circuitry that operates on an RF signal being received or transmitted. For example, the front-end circuitry may down-convert a received RF signal to baseband and/or up-convert a baseband signal for RF transmission.
The RF front-end circuitry typically includes analog circuits such as low noise amplifiers and mixers that have a relatively high sensitivity to noise and interference. The RF circuitry in some applications, such as in mobile communication cellular handsets, may be required to detect signals as small as a few micro-volts or less in amplitude. It is thus often important to minimize noise and interference from sources external or even internal to the communication apparatus.
Typical WCDMA (Wideband Code-Division Multiple Access) transceiver system architectures include separate receiver and transmitter chipsets. The main reason for implementing the receiver and transmitter circuits on different integrated circuits (ICs) is to avoid interference between the two circuits, since the receiver and transmitter are typically operating at the same time in WCDMA systems. However, despite integration of the receiver and transmitter circuits on separate ICs, typical transceiver systems may still suffer from transmitter feed through via the antenna.
To prevent or reduce transmitter feedthrough, typical WCDMA transceiver architectures may include two separate filtering stages in the receiver circuit. The first stage filtering is typically achieved via a duplexer and the second stage filtering is typically achieved through a surface acoustic wave (SAW) filter. In some systems, the SAW filter is implemented off-chip and may therefore increase the required pin count for the system.
Another problem that can sometimes be associated with typical WCDMA transceiver systems is power consumption. Most architectures include separate voltage-controlled oscillators (VCOs) for the receiver and transmitter circuits. Since VCOs are typically power hungry devices, these architectures can consume considerable amounts of power.